[Cake] and the bad cpu news on arm is

Björn Grönvall bjorngx at gmail.com
Sun Dec 20 03:55:14 EST 2015

Hi Dave,

The data cache on the wndr3800 and the archer is only 32k bytes. Some arm models also have a small cache.

Since the cake data structures are comparatively large it is important to only bring data into the cache that will actually make a difference when enqueueing.

The attached patch avoids reading data that will not be used. It will also save instructions when there are “q->way_hits”.

N.B. If your arm has a large data cache this change may not make much of a difference.


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On 19 Dec 2015, at 21:03, Dave Taht <dave.taht at gmail.com> wrote:

> is that bcake configured via sqm to do 200mbit/20mbit, rings
> in at 82% idle over a 2 minute period over a 1 minute rrul test.
> cake, in all it's glory of statistics, extra features, bells, and whistles...
> is also 82% idle.
> vs sqm's htb + fq_codel at 86% idle.
> (in other words, this is not a direct measurement of the code under
> 'load' but over a large sampling interval comparing idle with the
> loaded state, AND (sigh) htb + fq_codel uses less cpu. am using the
> mpstat 1 120 test for this from the openwrt sysstat package)
> The good news from my perspective:
> A) that it works at all with linux 4.4rc4 on the linksys 1200ac, which
> was certainly not the case til last week
> B) We CAN profile now
> C) All systems for bandwidth (htb and cake) are accurate to 200mbit at
> least, on this hardware
> The bad news from my perspective:
> A) I ran out of time for this back in august. Really have a ton of
> wifi work stacked up.
> B) I'd like to see someone show an instance where cake uses less cpu
> or is better in any way than htb+ fq_codel.
> There is a very small latency improvement (.8ms vs 1ms on this path).
> I do not see any other appreciable difference in cpu usage or network
> behavior... aside from negative ones.
> Someone that's saying "ooh cake's better" *please* go measure rrul_be
> while running "mpstat 1 120" for both sqm with fq_codel and sqm with
> cake.
> C) I will try to summon the energy to try it on mips myself, tomorrow.
> --
> Dave Täht
> Let's go make home routers and wifi faster! With better software!
> https://www.gofundme.com/savewifi
> _______________________________________________
> Cake mailing list
> Cake at lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cake


Björn Grönvall, bjorngx at gmail.com, Cell +46 70 768 06 35, Jabber/XMPP: bg at kth.se

“The ultimate tragedy is not the oppression and cruelty by the bad people but the silence over that by the good people.”

? Martin Luther King Jr.

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